On June 4, 1873, a squad of volunteer soldiers, under the command of the rebel priest Manuel Santa Cruz Loidi (pictured above), executed 37 border guards on the Endarlatza bridge between Gipuzkoa and Navarre during the Carlist War of 1872-1876. From that moment on the civil and military authorities in Gipuzkoa held annual remembrance services for those executed until the entry of Carlist forces into the province during the Spanish Civil War in 1936, when the service was suspended (despite the fact that during the nineteenth-century war Santa Cruz himself had been condemned to death on account of his sanguinary exploits by the very Carlist forces he purported to support). During that same Carlist War Sant Cruz’s squad carried a black flag with a skull and the inscription “Battle to the Death.”
Information sourced from Iñaki Egaña, Mil noticias insólitas del país de los vascos(Tafalla: Txalaparta, 2001), pp. 193.
The Carlist Wars are discussed in Cameron Watson’s Modern Basque History: Eighteenth Century to the Present, available free to download here.